ICDP workshop on scientific drilling of Lake Challa

Application deadline: 20 May 2012

The sediment record of Lake Challa (3Â°S, 38Â°E), a permanently stratified crater lake on the lower east slope of Mt. Kilimanjaro, has archived a uniquely long and continuous history of continental climate and ecosystem change in eastern equatorial Africa. Its location squarely inside the intertropical zone is highly appropriate to study long-term climate dynamics near the equator, because latitudinally extensive seasonal migration of the Intertropical Convergence Zone over East Africa generates strong regional interaction between north- and southeasterly monsoons. Lake Challaâs proximity to the Indian Ocean also ensures its all-season location east of the zone of convection between Atlantic and Indian Ocean moisture sources, such that the region is little affected by the climatic effects of changes in Atlantic meridional overturning circulation, through which signatures of northern high-latitude glaciation are imprinted on low-latitude continents.

Multi-proxy investigation of accurately-dated sediment cores covering the last 25,000 years confirmed Lake Challaâs potential as a tropical climate archive of global significance. Stimulated by seismic-reflection data of the deeper sediment sequence revealing an exquisite stratigraphy over at least 150,000 years, the DeepCHALLA research consortium is now preparing a drilling project to recover this long record. Selected research objectives are:

* To reconstruct a complete glacial-interglacial cycle of tropical monsoon dynamics over the western Indian Ocean, allowing assessment of the regional interplay between low-latitude insolation forcing and long-distance impacts of northern high-latitude and Antarctic glaciation. * To document long-term ecological dynamics of a tropical grassland-woodland landscape in response to changes in atmospheric CO2, temperature, moisture balance, and fire.

* To reconstruct the long-term dynamics of a tropical freshwater ecosystem in response to climate-driven changes in lake level, temperature, water-column mixing and nutrient budget.

An ICDP-funded workshop and fieldtrip to Lake Challa will be held in Nairobi and Taveta, Kenya, on 10-14 September 2012 to further develop the projectâs scientific goals and to discuss technical and logistic issues concerning recovery of the long sediment sequences and a lake-system monitoring program. It will also discuss the projectâs multi-national scientific collaboration and co-financing, and opportunities for outreach and knowledge transfer. The principal workshop outcome will be a draft science plan that will form the basis of an ICDP drilling proposal.